MEXICO CITY - Mexico's incoming president Andres Manuel Lopez Obrador on Friday slammed a decision by the electoral authority to fine his party $10 million over a campaign financing breach, calling it an "act of vengeance" against his landslide victory.

On Wednesday, the National Electoral Institute (INE) handed down the fine to Lopez Obrador's leftist National Regeneration Movement (MORENA) over a trust the party created last year, which the party said went to helping earthquake victims.

But the INE said MORENA was opaque about the money that came in and out and said the party broke the rules.

"This is an act of vengeance," Lopez Obrador said outside his team's offices in Mexico City, accusing the INE of behaving "tendentiously" and of overreaching.

"They're acting this way because they don't accept the new reality," the 64-year-old said, resorting to the sort of combative tone he used in the campaign to attack the government.